POS0818 IN PRIMARY SJÖGREN’S SYNDROME CCR9/CXCR5 CO-EXPRESSING EFFECTOR CD4 T CELLS ARE INCREASED AND ARE ENRICHED IN PD-1/ICOS-EXPRESSING T CELLS
Authors: A. Hinrichs, A. Kruize, F. Lafeber, H. Leavis, J. Van Roon
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Primary Sjögren's syndrome (pSS) is an autoimmune disease characterized by B cell hyperactivity. CXCR5+ follicular helper T cells (Tfh), CXCR5-PD-1hi peripheral helper T cells (Tph) and CCR9+ Tfh-like cells have been implicated in driving B cell hyperactivity in pSS (1-3), however, their potential overlap has not been evaluated. <h3>Objectives</h3> To study the overlap between the two CXCR5- cell subsets and to study their PD-1/ICOS expression, hall mark markers, as compared to "true" CXCR5/PD-1/ICOS-expressing Tfh cells. <h3>Methods</h3> We defined Tph cells as CXCR5-PD-1hi memory (CD45RO+), CCR9+ Tfh-like as CXCR5-CCR9+, and CCR9+ Tfh as CXCR5+CCR9+ memory CD4 T cells, as previously described. CXCR5+CCR9+ co-expressing cells were not specified on memory phenotype. Tfh cells were defined as CXCR5+ memory, and "true" Tfh cells as CXCR5+PD-1+ICOS+ memory cells. CXCR5- Tph and CCR9+ Tfh-like cell populations from peripheral blood mononuclear cells of pSS patients (n=12) and age- and gender-matched healthy controls (HC, n=11) were compared by flow cytometry. PD-1/ICOS expression from these cell subsets was compared to each other and to CXCR5+ Tfh cells, taking into account their differentiation status. <h3>Results</h3> In pSS patients the number of Tph cells was significantly increased compared to HC (median 0.53% versus 0.23% of CD4 T cells, p=0.049). Also the number of CCR9+ Tfh-like cells was significantly elevated in pSS patients as compared to HC, i.e. approximately 2.7% in pSS patients versus 1.7% in HC (medians, p=0.019). CCR9 expression was equally distributed between pSS patients and HC in Tph cells. Only a modest number of 2.1% (1.2-3.2%) of Tph cells expressed CCR9 (median with interquartile range), indicating limited overlap. CXCR5+ (Tfh) cells were characterized by the highest frequency of PD-1hi cells, either with or without CCR9 co-expression (PD-1hi expression differed between CXCR5+ T cell subsets compared to CXCR5-CCR9- and CXCR5-CCR9+ T cells, both p&lt;0.0001.) No difference in PD-1hi expression was seen between CXCR5+CCR9- and CXCR5+CCR9+ cells (p=0.57). Within the PD-1hi populations, cells expressing either CXCR5 and/or CCR9 of pSS patients showed a trend of higher ICOS expression compared to HCs, but this was only significant in CCR9+ Tfh-like cells (28.6% and 55%, medians for HC and pSS respectively, p=0.02) PD-1/ICOS expression was higher in memory cells expressing CXCR5 or CCR9. However, the highest expression was found in CXCR5/CCR9 co-expressing T cells, which are enriched in the circulation of pSS patients. PD-1, ICOS, and PD-1/ICOS co-expression was significantly higher on CCR9+ Tfh cells than on CCR9- Tfh cells (in all three comparisons p&lt;0.05). <h3>Conclusion</h3> CXCR5- Tph and CCR9+ Tfh-like cells are two distinct cell populations that both are enriched in pSS patients and can drive B cell hyperactivity in pSS. The known upregulated expression of CCL25 and CXCL13, ligands of CCR9 and CXCR5, at pSS inflammatory sites suggests concerted action to facilitate migration of CXCR5+CCR9+ T cells, which are characterized by the highest frequencies of PD-1/ICOS positive cells. Hence, these co-expressing effector T cells may significantly contribute to the ongoing immune responses in pSS. <h3>References</h3> [1]Chen W, Yang F, Xu G, Ma J, Lin J. Follicular helper T cells and follicular regulatory T cells in the immunopathology of primary Sjögren's syndrome. Journal of Leukocyte Biology. 2021 Feb 1;109(2):437–47. [2]Blokland SLM, Hillen MR, Kruize AA, Meller S, Homey B, Smithson GM, et al. Increased CCL25 and T Helper Cells Expressing CCR9 in the Salivary Glands of Patients With Primary Sjögren's Syndrome: Potential New Axis in Lymphoid Neogenesis. Arthritis &amp; Rheumatology. 2017 Oct;69(10):2038–51. [3]Pontarini E, Murray-Brown WJ, Croia C, Lucchesi D, Conway J, Rivellese F, et al. Unique expansion of IL-21+ Tfh and Tph cells under control of ICOS identifies Sjögren's syndrome with ectopic germinal centres and MALT lymphoma. Ann Rheum Dis. 2020;79:1588–99. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.